When the US military released a request for what would become the M1 Carbine in 1940, the Auto-Ordnance Corporation offered up a Thompson submachine gun simply rechambered for the new .30 Carbine cartridge. This entailed a new magazine, a receiver modified for the longer magazine, and a new barrel and bolt face – but the other Thompson parts could remain unchanged form the standard .45 ACP models. This made the submission a pretty cheap and easy effort for Auto-Ordnance…which is a good thing, considering that it was almost assured to be rejected.
The stipulations for the new carbine included a weigh requirement of 5 pounds, and the Thompson weighed more than double that (in both .45ACP and .30 Carbine forms). Only a few were made, and the one submitted for military testing was rejected outright on the basis of weight. This example is serial number 1, and resides at the Cody Firearms Museum.